OSTree is a tool that combines a "git-like" model for committing and 
downloading bootable filesystem trees, along with a layer for deploying 
them and managing the bootloader configuration.

OSTree is like git in that it checksums individual files and has a 
content-addressed-object store. It's unlike git in that it "checks out" 
the files via hardlinks, and they should thus be immutable. Therefore, 
another way to think of OSTree is that it's just a more polished 
version of Linux VServer hardlinks.

Features:
* Atomic upgrades and rollback for the system
* Replicating content incrementally over HTTP via GPG signatures and
  "pinned TLS" support
* Support for parallel installing more than just 2 bootable roots
* Binary history on the server side (and client)
* Introspectable shared library API for build and deployment systems

This last point is important - you should think of the OSTree command 
line as effectively a "demo" for the shared library. The intent is that 
package managers, system upgrade tools, container build tools and the 
like use OSTree as a "deduplicating hardlink store".
